The present invention relates generally to the fabrication of magnetoresistive (MR) and inductive recording sensors or transducers for data storage application. More specifically, the present invention relates to a method and apparatus for bending a bar which carries a plurality of sliders at multiple points during the fabrication process and specifically during the lapping process.
During the fabrication of magnetic heads for use in magnetic data storage applications, an array of transducers are fabricating on a common substrate (also called a wafer) by depositing a plurality of layers onto a surface of the substrate. The array of transducers are patterned using, for example, a photolithographic process in combination with various etching and liftoff processes. The finished substrate or wafer is then optically and/or electrically inspected and subsequently cut into smaller arrays, typically a plurality of bars, i.e. rows of transducers. Next, the individual rows or bars of transducers are machined or "lapped" to obtain a desired dimension. (Lapping is a material removal process described below in more detail.) For MR transducers, this dimension is sometimes referred to as stripe height (SH) and for inductive transducers this dimension is sometimes referred to as throat height (TH). Often, electrical lap guides (ELGs, described below) are deposited upon the same substrate and are used as sensors during the lapping process. Following the lapping process, the recording heads are diced to produce individual transducers or heads which are used to form sliders. These sliders are used to read back and/or write information onto a surface of a magnetic disc, for example, which moves at a high rate of rotation.
In order to establish adequate performance for high efficiency recording heads, it is necessary to achieve the desired stripe height or throat height. There are many factors which affect variations in the ultimate stripe height or throat height. These factors include variations in the position and size of elements induced during wafer processing. The step of slicing the substrate into bars can also introduce variations. Mounting induced thermal stress can also cause variations during the processing of the wafers into sliders. Further, the profile of the lapping surface can lead to variations.
Electrical lapping guides (ELGs) are sensors which are deposited onto the wafer during the fabrication process. The output from the ELGs can be used to determine when to stop the lapping process. Typically, the ELGs are fabricated along with the transducers using the same wafer processing steps. This is described, for example, in U.S. Pat. No. 4,477,968 which issued Oct. 23, 1984 and U.S. Pat. No. 4,559,743 which issued Dec. 24, 1985.
Lapping generally refers to machining processes in which material is very slowly, at a controllable rate, removed from a surface. Typically, the process involved applying a work surface of the work piece to a moving surface which is slightly abrasive. One such device is described in U.S. Pat. No. 4,536,992 which issued Aug. 27, 1985. Thus, by controlling the lapping process in response to the output from the ELGs, a closed loop machining process is set up in which the output from the ELGs are used as feedback to the lapping machine.
During the lapping process, the slider is held on a carrier which attaches to the arm of the lapping apparatus. Such a carrier is described in U.S. Pat. No. 4,457,114 which issued Jul. 3, 1984. The carrier in U.S. Pat. No. 4,457,114 uses two actuators to bend the bar during the lapping process. In U.S. Pat. No. 4,457,114, the carrier provides bending of the bar at both ends around the center of the bar. This bending is used to provide non-uniform removal of material from the bar in order to compensate for variations in the bar and the throat height or stripe height of the sensor. In U.S. Pat. No. 4,457,114, the actuators comprise pins which are heated to thereby expand and apply a force to the bar which bends the bar. A variation on this technique is to use three different actuators to apply force to a bar at three different points.
Generally, the prior art has focused on improved ELGs and lapping mechanisms. However, as the data storage industry is continuously driven to higher and higher densities and in an ongoing effort to reduce costs of fabrication, a number of competing factors are observed. First, the sensor height tolerance requirement is getting smaller. Second, the density of heads carried on each bar is getting larger. Third, the aspect ratio of the length to the thickness of each bar is getting larger. Therefore, existing lapping and bending systems are often inadequate for controlling the lapping process. These factors not only lead to heads which are more sensitive to processing induced disturbances, but also lead to bars which are more easily disturbed because they are thinner and the stiffness of the bar is related to the cube of its thickness.